# Aizu Problem ITP_1_10_A: Distance
#
import sys, math, os

# read input:
PYDEV = os.environ.get('PYDEV')
if PYDEV=="True":
    sys.stdin = open("sample-input.txt", "rt")


x1, y1, x2, y2 = [float(_) for _ in input().split()]
print("%.8f" % math.sqrt((x1 - x2)**2 + (y1 - y2)**2)) import sys, math, os sys math os PYDEV = os.environ.get('PYDEV') PYDEV os.environ.get('PYDEV') os.environ.get os.environ os environ get 'PYDEV' if PYDEV=="True":
    sys.stdin = open("sample-input.txt", "rt") PYDEV=="True" PYDEV "True" sys.stdin = open("sample-input.txt", "rt") sys.stdin sys stdin open("sample-input.txt", "rt") open "sample-input.txt" "rt" float(_) for _ in input().split() for _ in input().split() _ input().split() ().split () input split for _ in input().split() float(_) float _ x1, y1, x2, y2 = [float(_) for _ in input().split()] x1 [float(_) for _ in input().split()] y1 x2 y2 print("%.8f" % math.sqrt((x1 - x2)**2 + (y1 - y2)**2)) print "%.8f" % math.sqrt((x1 - x2)**2 + (y1 - y2)**2) "%.8f" math.sqrt((x1 - x2)**2 + (y1 - y2)**2) math.sqrt math sqrt (x1 - x2)**2 + (y1 - y2)**2 (x1 - x2)**2 x1 - x2 x1 x2 2 (y1 - y2)**2 y1 - y2 y1 y2 2 x2, y2 = [float(_) for _ in input().split()] [float(_) for _ in input().split()] x2 PYDEV = os.environ.get('PYDEV') os.environ.get('PYDEV') PYDEV y2 = [float(_) for _ in input().split()] [float(_) for _ in input().split()] y2 y1, x2, y2 = [float(_) for _ in input().split()] [float(_) for _ in input().split()] y1 x1, y1, x2, y2 = [float(_) for _ in input().split()] [float(_) for _ in input().split()] x1
# Aizu Problem ITP_1_10_A: Distance
#
import sys, math, os

# read input:
PYDEV = os.environ.get('PYDEV')
if PYDEV=="True":
    sys.stdin = open("sample-input.txt", "rt")


x1, y1, x2, y2 = [float(_) for _ in input().split()]
print("%.8f" % math.sqrt((x1 - x2)**2 + (y1 - y2)**2))